Preheat the oven to 180°C. Grease 4 small baking tins or a large ovenproof dish with nonstick spray.
1. Mix the sweet potato and dates, sprinkle the bicarbonate of soda over and pour the first lot of boiling water or tea over. Leave to cool.
2. Whisk the eggs and butter, add the cocoa powder, salt and baking powder and mix well. Add to the sweet potato mix.